The MUYA EZ-9909 is a compact, pen-style 5-in-1 water quality meter that measures TDS, EC, pH, salinity, and temperature in a single test. It covers a wide working range -- pH 0.01-14.00, EC up to 400 mS/cm, TDS up to 200 ppt, and salinity up to 25% -- with automatic temperature compensation and calibration support for accurate readings in aquariums, hydroponics, pools, and general water testing. Its IP67 waterproof housing, backlit display, adjustable TDS conversion factor, and auto power-off make it a durable, easy-to-carry field instrument.